1. Technical Field
The present invention relates to a method for forming a deposit, a droplet ejection apparatus, an electro-optic device, and a liquid crystal display.
2. Related Art
A procedure for manufacturing a display or a semiconductor device includes a number of steps of forming a patterned film. Specifically, the patterned film is formed by depositing a film on a substrate and subjecting the film to patterning in a predetermined shape.
To improve productivity, this type of process for forming a patterned film now employs an inkjet method. In the method, a patterned film is formed by ejecting droplets of liquid onto a substrate and solidifying the droplets on the substrate. The patterned film is thus formed on the substrate in correspondence with the shapes of the droplets. This makes it unnecessary to form a mask for patterning, thus decreasing the number of the steps for forming the patterned film.
However, in formation of the patterned film by the inkjet method, some of the ejected droplets may not spread wet and form recesses and projections on the surface of the substrate. The patterned film reflects the recesses and projections, thus causing unevenness in the patterned film or non-uniform thicknesses of the patterned film.
To solve this problem, a method for promoting wet spreading of the droplets on the surface of the substrate has been proposed. As described in JP-A-2005-131498, droplets of liquid are ejected in a direction inclined with respect to a normal line of a substrate. This provides a velocity component in a direction along tangential line of the substrate to each of the ejected droplets. The droplets thus effectively spread wet along the surface of the substrate at an angle (an inclination angle) defined by the normal direction of the substrate and the ejecting direction of the droplets.
To change the thickness of the patterned film formed by the inkjet method, or to change the total ejection amount per unit area, the ejection pitch of the droplets, normally, is altered while the volume of each droplet is maintained at a constant value. For example, to form a patterned film having a relatively small thickness, the volume of each droplet is maintained constant. However, the ejection pitch of the droplets is increased by raising the scanning speed of the substrate with respect to the nozzles or prolonging the operation cycle of ejection. This stabilizes ejection of the droplets, ensuring reproducibility of the total ejection amount, or reproducibility of the thickness of the patterned film.
However, the technique of JP-A-2005-131498 addresses only to offset traveling and splash of ejected droplets. The inclination angle of the ejecting direction is selected from a relatively large range. Therefore, as illustrated in FIG. 10, if the inclination angle θ of the ejecting direction A is excessively small when forming a patterned film with a relatively small thickness by increasing the ejection pitch W of the droplets Fb, the on-substrate size R1 of each droplet Fb on the substrate becomes smaller than the ejection pitch W of the droplets Fb. Thus, the droplets Fb are scattered on the substrate.
As a result, unevenness of the droplets Fb is reflected in the shape of the obtained patterned film, causing significant non-uniformity in the thickness of the patterned film.